It looks like you &/or your mechanic already checked the wiring but there are 2 that I would recheck for continuity & shorting to ground.
1st is the black wire that runs from PCM terminal 7 to ICM terminal F.
2nd is the Brown/White wire that runs from Crank Sensor terminal A to ICM terminal J.
For both continuity & shorting to ground you'll be checking resistance (ohms). After disconnecting the wiring harnesses from PCM, ICM & Crank Sensor connect the meter leads to both ends of the black wire & then the brown/white wire. Post the results for us but both wires should have very low resistance. To check for a short to ground connect one meter lead to something metal on the engine & the other lead to either end of the black then brown/white wire. Both readings should be near infinity.
Edit - before reconnecting the wiring harnesses check both the female & male ends of all the connections for any signs of corrosion & bent or broken pins. Examine #7, F, J & A very carefully.
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1997 Chevy Lumina (daughter'*)
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